Researchers agree that for children who attend early care and education programs, high-quality early learning experiences are critical for promoting academic, social-emotional, and executive function skills, particularly for children of color and children from families with low incomes. Rigorous research testing the effects of interventions to enhance classroom quality has found that providing professional development to teachers, including ongoing training and coaching, can improve classroom quality and teachers' instructional practices as well as children's outcomes. These benefits are particularly noticeable when professional development is focused on a specific curriculum or set of teacher practices. Yet, again, questions remain. When and for which children do quality enhancement efforts have the most impact? When and for which early care and education centers and teachers can quality enhancement efforts be implemented successfully? Answering these questions will help the early care and education field target investments in ways that are more likely to support classroom quality and help all children succeed. The "Variations in Implementation of Quality Interventions (VIQI): Examining the Quality-Child Outcomes Relationship in Child Care and Early Education" project aims to tackle these open questions and build substantial new evidence to inform policies and practices in Head Start and community-based child care centers. The VIQI project is a large-scale, rigorous study that examines the link between classroom quality and preschool children's developmental outcomes. It builds on and extends prior research--including the "Child Care and Early Education Quality Features, Thresholds and Dosage and Child Outcomes (Q-DOT) project." This prior work suggests that when classroom quality is in the higher portion of the quality range, links between quality and children's outcomes are stronger than when classroom quality is in the lower portion of the quality range. This brief describes the VIQI project, its key research questions, and the conceptual framework underlying it.